(a) Field of the Invention
The present invention concerns the preparation of disilane.
(b) Description of Prior Art
Generally, the SiCaAl alloy is reacted with a dilute solution of hydrochloric acid to give a mixture of monosilane, disilane and trisilane, with impurities such as phosphine, hydrogen sulfide, arsine, disiloxane and higher siloxanes, after which the disilane is extracted from the mixture by distillation.
However, the process of distillation does not enable separation of disiloxane from disilane since the vapor tension curves of these two compounds are practically confounded. On the other hand, the distilled disilane still comprises traces of phosphine, hydrogen sulfide, and arsine, with contents in the order of 10 ppm. It is therefore necessary to provide a complementary purification process so as to obtain disilane of satisfactory purity for electronic applications.
For this purpose, it was suggested to use a final separation by adsorption on molecular sieves, but the first studies that the Applicant has carried out have shown that the separation on molecular sieves could lead to a decomposition of disilane when in contact with the sieve, which could result in a loss in the order of 20%, without being successful in achieving a nearly complete elimination of the impurities, so that the final quality of the product does not meet the norms that the electronic industry requires.